Empirical relations between incident solar radiation received at the earth's surface and (1) percent of possible sunshine, (2) latitude, and (3) time of year are developed. These relations are combined into a graphical method for converting percent of possible sunshine into daily values of incident solar radiation for stations between latitudes 25° N. and 50° N. The method is tested on independent data from widely separated locations and a correlation coefficient of 0.97 between estimated and observed values is obtained.